1. Field of the Invention
The invention concerns the observation of very rapid luminous or light phenomena.
2. Description of the Prior Art
Ultra-fast recording cameras are used to observe these phenomena. These ultra-fast cameras are adapted to the high rate of the images to be analyzed and to the light flux available for each image.
If the phenomena to be analyzed occur very rapidly, the image periods become very short and the light flux of each image also becomes very low as a rule.
It then becomes necessary to introduce one or more image intensifiers into the chain of analysis. This enables the obtaining of a sufficient output signal which goes, either to a photographic film or to an image analyzer (television camera tube or charge transfer device for example).
The difficulty that arises is the following one: the pictures succeed one another very quickly, at a rate that is greater than the possibilities of analysis of the images at the output of the television camera. It is therefore sought to select certain images that are more useful than others, and the effort of analysis is concentrated on these pictures. However, for this, there should be the ability to make a very fast selection of the useful image among the images which go past at high speed and to direct the useful image towards means of analysis, in eliminating the other ones.
To illustrate the problem in concrete terms, we shall give a numerically illustrated example in a context where it is sought to analyze pictures coming from the detection of collisions of particules accelerated in an accelerator used for studies in nuclear physics, these collisions being displayed by means of scintillators.
The light images are observed in several directions and it is sought to analyze images at regular periods of about 10 nanoseconds.
However, all the images do not need to be recorded definitively with a view to very intensive analysis. Besides, this could not be done in view of the enormous quantity of information represented by the fact that there is an image every 10 nanoseconds, especially if, in practice, a simultaneous recording is made of a large number of images resulting from the observation of the phenomenon in a large number of different directions.
Consequently, the useful images are selected in order in order to be recorded. For this, a computer gives an indication on the need to make a special analysis of such and such an image. However, it cannot give this indication immediately. It gives it, for example, with a delay of one microsecond.
It is therefore necessary to temporarily store about a hundred images when the computer decides that one of them is useful and should be permanently recorded or sent towards means of analysis.
A possibility could be envisaged where the arrival of the images coming towards the television camera or image intensifier would be delayed by one microsecond, so that the images to be intensified would be received synchronously with a signal indicating that such and such an image is useful and should be stored with a view to analysis. For this purpose, it is possible to simply provide for optic fibers between the production of light images and the camera, these optic fibers being long enough to delay the transmission of the image. Calculations show that, to delay the images by one microsecond, there should be a fiber length of at least 200 meters, thus raising difficult problems when there are tens of thousand of fibers which undergo the same delay.
The other idea that comes to mind is that of routinely recording all the images that arrive during the period of one microsecond. At the end of this period, a validation signal, indicating that a useful image has to be analyzed, is either received or not received. If this signal is received, the useful image is preserved and the others are eliminated. If no validation signal is received, the images are eliminated, and the system again becomes available to receive a fresh sequence of images. However, there is no way known to make very high speed recordings of a large quantity of images: the figure of 100 images to be recorded with a camera during a period of one microsecond is not realistic at the present time.